Title 2. MOTION IN A STRAIGHT LINE.pdf ✅

Oswaal CBSE Question Bank Chapterwise & Topicwise, PHYSICS, Class-XI (b) Motion in 2–D (i) If two out of three coordinates specifying the position of the object change with respect to time, the motion is called 2–D motion. (c) Motion in 3–D (i) If all the three coordinates specifying the position of the object change with respect to time, the motion is called 3–D motion.  Path Length or Distance : (a) Path Length is defined as the actual path traversed by body during motion in a given interval of time. (b) Distance is a scalar quantity. (c) The S.I. unit of distance is metre and C.G.S. unit is centimeter. (d) The value of distance traversed by a moving body can never be zero or negative.  Displacement : (a) Displacement of a body in a given time is defined as the change in the position of the body in a particular direction during that time. It may also defined as the shortest distance between initial and final position of the object. (b) Displacement is a vector quantity as it possesses both magnitude and direction. (c) The unit of displacement is same as that of path length. (d) The value of displacement can be positive, zero or negative. (e) The value of displacement can never be greater than the distance travelled. (f) When a moving body returns to its starting point, then its effective displacement is zero.  Difference between Distance & Displacement : S. No. Distance Displacement 1. Actual path traversed by object in given time. Shortest distance between initial & final positions of object in given time. 2. Scalar quantity. Vector quantity. 3. It cannot be zero or negative, it will be always positive. It can be positive, negative or zero. 4. It is either equal or greater than displacement but never less than displacement. It is either equal or less than distance but never greater than distance. 5. It can have many values depending upon path followed between two positions. It has unique value. 6. Between two positions of an object, it tells type of path followed. It does not tell type of path followed.  Instantaneous velocity : If a body is moving with a variable velocity, then the velocity of the body at a given instant of time is called its instantaneous velocity. Key Words  Uniform motion is said to be in an object when velocity is uniform i.e., it undergoes equal displacements in equal intervals of time, howsoever small these intervals may be.  Non–uniform motion is said to be in an object when it undergoes equal displacements in unequal intervals of time, howsoever small these intervals may be. Mnemonics Concept: Motion In A Straight Line Mnemonics: Delhi to Vadodara via Tundla Agra. Interpretation: Displacement/time = Velocity Velocity / time = Acceleration Key Formulae 3⁄4 Path length or distance, D = Speed × Time 3⁄4 Displacement = Velocity × Time

CBSE Question Bank Chapterwise & Topicwise, PHYSICS, Class-XI Short Answer Type Questions-II (3 marks each) Q. 1. An object moving on a straight line covers first half of the distance at speed v and second half of the distance at speed 2v. Find (i) average speed, (ii) mean speed. A [NCT 2011] Ans. Let total distance be x. Distance of first half = 2 x speed = v Time taken, t 1 = 2 2 = x x v v Distance of second half = 2 x speed = 2v time taken, t 2= 2 2 4 = x x v v 1 (i) Average speed = Total distance travelled Total time taken = 4 2 4 x v x x 3 v v = + 1 (ii) Mean speed = 2 3 2 2 + = vv v 1 Commonly Made Error Students may commit mistake while calculating the total time taken in the given problem. Answering Tip Students should assume the distance appropriately and then calculate the required quantities by taking LCM correctly. Long Answer Type Questions (5 marks each) Q. 1. Define displacement. What are its characteristics ?R Ans. Refer to ‘Revision notes‘. 5 Q. 2. Define the following terms : (a) Speed, (b) Uniform speed, (c) Variable speed, (d) Average speed, (e) Instantaneous speed, (f) Velocity, (g) Uniform velocity, (h) Variable velocity, (i) Uniform motion, (j) Instantaneous velocity. R Ans. Refer to ‘Revision notes‘. 5 Q. 3. What are the important points about the uniform motion ? R Ans. Following are some important points about the uniform motion : (i) The velocity in uniform motion does not depend upon the time interval (t 2 – t 1 ). 1 (ii) The velocity in uniform motion is independent of the choice of origin. 1 (iii) No force acts on the object having uniform motion. 1 (iv) Velocity is taken to be positive when the object moves towards right of the origin and it is taken negative if the object moves towards left of the origin. 2 Topic-2 Uniformly Accelerated Motion Revision Notes  Accelerated motion : When an object is moving in non-uniform motion, the velocity is different at different instants i.e., the velocity keeps on changing with time. This motion is an accelerated motion.  Acceleration : It is defined as the ratio of change in velocity & the corresponding time taken by the mirror object; (a) It is vector quantity. (b) It is either positive or negative. (c) Negative acceleration is called retardation. (d) Unit-m/s2 in SI & cm/s2 in CGS system.